Transition element

A transition element is a metal in the central block of the periodic table, such as iron, copper or zinc, with characteristic special properties like variable oxidation numbers, coloured compounds and catalytic activity. Malay: unsur peralihan · Chinese: 过渡元素.

The transition elements sit between Group 2 and Group 13, and they behave differently from the main-group metals because their electrons fill an inner shell as they cross the block. The syllabus expects you to know their four special properties: they show more than one oxidation number (a variable oxidation number), they and their compounds often act as catalysts, they form coloured compounds and coloured ions, and they readily form complex ions. All four are what set a transition metal apart from a Group 1 or Group 2 metal.

Example. Iron shows two oxidation numbers, forming Fe²⁺ (pale green in solution) and Fe³⁺ (yellow-brown), and it acts as a catalyst in the Haber process. Copper forms blue Cu²⁺ compounds, and manganese and its compounds appear in several oxidation states. These coloured, variable, catalytic behaviours are the transition-element signature, and they are the properties an exam question will ask you to list and illustrate with named metals such as iron and copper.

Confusion to avoid. Do not treat a transition metal like a Group 1 metal: alkali metals have a single fixed oxidation number of +1, whereas a transition element can show several. Also, “transition element” is not just any metal, it means specifically the central-block metals with these special properties, not the reactive metals of Groups 1 and 2.

In the Periodic Table of Elements chapter the transition elements are the contrast case that sharpens the main-group rules: seeing why iron is coloured and variable while sodium is not helps fix what makes each part of the table behave as it does. Learning the four special properties as a short list, each tied to a named example, is the most reliable way to earn these marks.